Updated: Friday, September 6th, 2013 at 10:01pm

The U.S. decision not to challenge Washington and Colorado’s plans to legalize marijuana makes the U.S. drug policy look like a textbook case of political hypocrisy: How can the U.S. government give a green light to legalization at home while continuing to fight it abroad?

Last week, the U.S. Justice Department issued a ruling telling federal prosecutors not to interfere with the two U.S. states that have passed laws allowing the recreational use and sale of marijuana starting next year. The ruling has been hailed by pro-legalization forces as historic, since marijuana continues to be an illegal drug under federal laws.

In its memo Thursday, the Justice Department told prosecutors not to challenge the two states’ pot legalization laws as long as they impose a strict regulatory system that prohibits among other things the sale of marijuana to minors, the cultivation of marijuana on public lands and its export to other states that have not legalized it.

“This puts the United States in an awkward position in respect to its drug war export policy,” says John Walsh, a drug expert with the Washington Office on Latin America, a group that supports pot legalization. “The United States is going ahead with a policy that is quite different from what it tells other countries to do.”

It’s a policy decision that is likely to have a big impact in Latin America, where many countries are debating their own drug legalization laws.

In Uruguay, the Chamber of Deputies has already approved a government-supported marijuana legalization bill, which is likely to be approved by the Senate before the end of the year. Now, with the latest U.S. Justice Department decision, its Senate approval may be even easier than previously expected.

In Mexico, where more than 50,000 people have died in the U.S.-backed war on drugs over the past six years, legalization supporters in Congress will have additional arguments to back their stands. Why should we continue to spend money and lives to eradicate marijuana crops and to seize the drug before it reaches the U.S. border, when the United States has stopped fighting this war at home? they will ask.

Mexico is by far the biggest exporter of marijuana to the United States, and where the Justice Department ruling may have the biggest impact. Other major pot exporters in the region are Jamaica, Canada and Colombia.

Asked about the contradiction in U.S. domestic and foreign drug policies, a State Department spokesman told me that “marijuana is and remains illegal under federal law. We continue our important counternarcotics cooperation with the international community to combat drug trafficking and use, and to improve citizen security.”

U.S. officials suggest that it’s important to remember that the recent Justice Department decision is conditioned on Washington state and Colorado’s ability to effectively police themselves. Internationally, it’s not that clear that countries with weak institutions will be able to do that, and prevent, among other things, sales of marijuana to minors, legalization critics say.

As Uruguayan Sen. Pedro Bordaberry, an opponent of his country’s pot legalization bill, told me recently, “If Uruguay cannot even effectively enforce its prohibition to re-sell tickets for soccer matches, how can we expect it to enforce prohibition of marijuana sales to minors?”

My opinion: The Justice Department’s decision not to challenge the Washington state and Colorado legalization laws will go down in history as a turning point in the four-decade-old U.S. war on drugs.

There is no question legalization of marijuana makes more sense in Colorado or Washington state, where the police may be able to prevent pot sales to children or drugged driving, than in Guatemala or Honduras, where the police can often not even be trusted to be on the right side of the law.

But, in light of the latest Justice Department decision, the current U.S. drug policy is unsustainable.

The Obama administration should drop its blanket opposition to foreign countries’ marijuana legalization laws. It should do so in exchange for international agreements to enforce strict regulations on the marijuana business, including commitments to invest savings from marijuana eradication into anti-drug education campaigns and drug prevention and rehabilitation programs.